This invention relates in general to heating, ventilating, air conditioning, and refrigeration (HVAC-R) systems. In particular, this invention relates to an improved HVAC-R system structure and an improved method of simultaneously controlling an expansion valve in an HVAC-R system to achieve improved cooling of an evaporator, and a flow control valve in the HVAC-R system to improve operation of a condenser.
In some conventional HVAC-R systems, an expansion valve is controlled based on the superheat. Superheat control is achieved using pressure sensor and a temperature sensor to measure HVAC-R system fluid pressure and temperature, respectively. Superheat is then calculated for a particular refrigerant using the measured temperature and pressure, and controlled by causing the superheat to move to a target superheat value by adjusting the pressure and temperature using any of a group of known open-loop or closed-loop algorithms.
Superheat is a function of pressure and temperature, and is conventionally calculated using pressure-temperature (P-T) charts that map a saturation temperature at a particular pressure. The values of the saturation temperatures at particular pressures may vary with different refrigerants. These values for saturation temperature and a temperature of the refrigerant are typically measured at an outlet of an evaporator in the conventional HVAC-R system, and are typically used to calculate superheat.
In other known HVAC-R systems, a refrigerant charge is used to control the sub-cooling before the HVAC-R system is started. While the HVAC-R system is in operation the refrigerant charge cannot be added or removed. Thus, the sub-cooling may not be optimized while system is in operation. Sub-cooling may also be calculated for a particular refrigerant using the measured temperature and pressure, and may be controlled by causing the sub-cooling to move to a target sub-cooling value by adjusting the pressure and temperature using any of a group of known open-loop or closed-loop algorithms.
Sub-cooling is a function of pressure and temperature, and may be conventionally calculated using pressure-temperature (P-T) charts that map a saturation temperature at a particular pressure. The values of the saturation temperatures at particular pressures may vary with different refrigerants. These values for saturation temperature and a temperature of the refrigerant are typically measured at an outlet of a condenser in the conventional HVAC-R system, and are typically used to calculate sub-cooling.
It would be desirable however, to provide an improved HVAC-R system structure and an improved method of controlling the expansion valve by controlling sub-cooling at an outlet of the condenser and controlling superheat at an outlet of the evaporator.